WO2005097915A2

WO2005097915A2 - Interference pigments based on silicon or the alloys thereof

Info

Publication number: WO2005097915A2
Application number: PCT/FR2005/000535
Authority: WO
Inventors: Aurélie FAY; Patricia Dufour Tarrare
Original assignee: Invensil
Priority date: 2004-03-12
Filing date: 2005-03-07
Publication date: 2005-10-20
Also published as: FR2867483A1; WO2005097915A3

Abstract

The invention relates to metallic pigments which are provided with an interference colour and obtainable by treating metallurgical silicon or alloys based thereon or a ferrosilicon-based powders having flake shaped grains. The treatment is carried out in a dry (optionally with oxygen addition) or humid (addition of water) oxidising medium at a temperature ranging from 900 to 1350°C for a time ranging preferably from 5 minutes to 9 hours which are selected in such a way that a desired colour is obtainable. The inventive pigments exhibit a conventional metallic or iridescent aspect and are dispensed with usual addition of other colorants. The production of said pigments is particularly inexpensive and they exhibit an excellent corrosion resistance in acid, basic or salt media at temperatures up to 600°C.

Description

Interference pigments based on silicon or silicon alloys.

Field of the invention

The invention relates to the field of metallic coloring pigments and more specifically metallic powders having a tint by interference of light rays on their surface covered with an oxide.

The article in the book “Engineering techniques” AMI, page A3 233, by R. DEFOSSE distinguishes three families of pigments: - Mineral pigments (example TiO2), - Organic pigments, - Special pigments.

Metallic pigments, although they can, strictly speaking, by their nature, be considered as mineral pigments, are classified in the latter category.

State of the art

A pigment is a coloring matter, or providing a “metallic” or “iridescent” appearance, in the form of a powder (colored, white or black), and insoluble, unlike the “dyes” proper, in solvents and substrates.

The term “metallic pigment” covers powders based on aluminum, magnesium, copper, iron (steel), bronze, titanium or micaceous derivatives, used as additives, in particular paints and inks. The physical parameters influencing the “metallic” appearance imparted by said pigments are the average dimensions of the particles constituting the powder, their shape, their distribution and their orientation in the final formulation.

They generally have a particle size of between 5 and 25 μm and a form called flat scales or flakes or even micro-lamellae and are subdivided into two types, according to their behavior at wetting in solvents: - The filming pigments (or leafing) which remain on the surface of the formulation and are oriented parallel to the interfaces, forming a dense metallic layer which gives the medium a very high reflecting power and excellent protection. - Non-filming pigments which are oriented more or less parallel to the substrate, in a random manner and at the bottom of the preparation layer.

Their main applications are: - Coating paints and protection against corrosion, Paints giving a metallic appearance or “metallic paints”, - Inks for screen printing, gravure printing and flexography.

Thus, application CN 1412259 from "Zuanquian Huatai Industry", filed in 2001, describes the use of powders of silicon, aluminum and titanium dioxide, associated with an epoxy resin and diluting agents, as protective coatings for screws. against corrosion in a marine atmosphere. The same applies to the two Japanese patents JP 61-118470 and JP 61-118471 jointly filed in 1984 by "Dainippon Toryo" and "Mitsubishi Métal" and relating to paints containing metallic powders (copper, nickel, aluminum, silicon) to improve corrosion resistance. The second provides for the possibility of adding a coloring pigment. Finally, patents EP 1006156 and EP 1167398 of "Mitsubishi Rayon" filed in 1998 and 2000, relate to "anti-fouling" paints containing organic silicon compounds, in particular dimethylpolysiloxane. The term "anti-fouling" means anti-aging or anti-fouling ... Problem raised

The metallic pigments described in the prior art are mainly used to give the formulations a metallic or iridescent appearance. To obtain a possible color, the addition of other pigments or dyes is necessary. However, titanium powders, for example, can be colored by forming an oxide film on the surface of the grains, having a color by interference of the light rays on their surface. We then speak of effect pigments and interference color.

However, metals are mostly very sensitive to oxidation phenomena, possibly violent for powders of small particle size (risk of explosion), and accentuated by any acidity or alkalinity of the environment. The reactions governing these phenomena are generally inhibited by using oils, waxes, aqueous binders or shellac, which have the effect of physically isolating the metals from the ambient air and from humidity. Obviously, this addition constitutes an additional constraint for the manufacture and use of these pigments.

In addition, it should be noted that the metallic pigments known from the prior art (reference: Schieck R., Pigments, in Encyclopedia of chemical technology, vol. 17, 1982, p. 788) are aluminum-based powders , magnesium, copper, iron (or steel), bronze, titanium, or even micaceous derivatives. Metallurgical silicon, for its part, does not appear in this list. Patent EP 0 803 549 of "Ciba Specialties Chemicals Holding", filed in 1997, claims a coloring pigment consisting of a transparent, or reflective metallic core, coated with a layer of at least one silicon oxide, including stoichiometry in oxygen relative to silicon varies from 0.25 to 0.95, the deposition being able to be carried out by atomization or chemical vapor deposition (CND) of silicon in an atmosphere containing oxygen at low vapor pressures. The object of the invention is to obtain a colored metallic pigment which does not require the use of an additional dye, from powder based on silicon, or ferro-silicon, of metallurgical quality and under processing conditions. very simple industrial work.

Object of the invention:

The subject of the invention is a metallic pigment, having a tint by interference of light rays on its surface, or interference color, essentially consisting of a powder of metallurgical silicon or of alloys based on metallurgical silicon containing at least 60% in weight of silicon metal, or ferro-powder metallurgical silicon, one or the other powder being obtained by grinding and its grains being in the form of flakes covered with an oxidized layer. Preferably, the scales have a length of 1 to 250 microns, a width of 1 to 250 microns and a thickness of 0.1 to 10 microns. Advantageously, said metallurgical silicon contains at least 90% by weight of metal silicon, and preferably 97%, and said ferro-silicon contains between 5% and 75% by weight of iron, preferably between 25 and 35%.

According to a preferred embodiment, the oxidized layer has an average thickness of 10 nm to 1 μm. Finally, advantageously, the color of the pigment: is not altered by being kept in media with pH values between 1 and 14, is not altered by being kept at temperatures less than or equal to 600 ° C., Is not affected by corrosion in a saline environment.

The invention also relates to a process for treating a powder essentially consisting of metallurgical silicon or of alloys based on metallurgical silicon containing at least 60% by weight of silicon, or of metallurgical ferro-silicon, in order to obtain said metallic pigment, characterized in that it comprises the steps of: Preparation of a powder essentially consisting of metallurgical silicon or of alloy based on metallurgical silicon or metallurgical ferro-silicon, with a particle size between 1 and 250 μm, by grinding with l using ball mills, bars or cylinders, Maintaining this powder at a temperature of 900 to 1350 ° C in an atmosphere containing one or more oxidizing elements, the temperature, the duration of the treatment and the quantity of oxidizing elements being selected to obtain the desired color. Said atmosphere containing one or more oxidizing elements can be according to one of the following advantageous modes: Air with addition of oxygen, Air with addition of water, Air with addition of CO ₂ . Preferably maintaining temperature is between 1 min and 9 hours.

The invention also relates to the use of said pigments for the coloring of paints, lacquers for the automobile, plastics, glasses, ceramics, cosmetic and decorative products, or for the manufacture of paints or anti-corrosion materials and / or anti-fouling.

Description of the invention:

The invention is based on the observation made by the applicant that it is possible to apply a thermal oxidation treatment on a powder essentially consisting of metallurgical silicon or alloys based on metallurgical silicon or metallurgical ferro-silicon, in presence of one or more oxidizing elements, to obtain certain colors of these metallic effect pigments, that is to say having a tint by interference of light rays on their surface, or interference color.

The term “alloy based on metallurgical silicon” is understood to mean an alloy mainly containing metallurgical silicon. More precisely, this result is obtained by placing in a metallurgical silicon powder, containing at least 90% by weight of silicon, preferably at least 97%, or a powder of an alloy based on metallurgical silicon containing at least 60% by weight of silicon, or a ferro-silicon powder containing between 5 and 75% by weight of iron, preferably between 25 and 35%. The powder introduced has a particle size between 1 μm and 250 μm in length, 1 μm and 250 μm in width and 0.1 to 5 μm in thickness. The grains are in the form of micro-lamellae or scales. They are obtained by grinding crushed blocks typically using ball, bar or cylinder mills. The elongation of the grains is between 2 and 3. The sphericity of the grains is generally between 0.2 and 0.3. The form factor is around 0.5. The oven temperature is maintained between 900 ° C and 1350 ° C. The exposure times, that is to say keeping the temperature, to obtain a given color, depend on the temperature and are between 1 minute and 9 hours. The higher the temperature, the shorter the exposure time, to obtain the same given color.

Oxidation can be carried out dry (air or air with addition of oxygen), wet (air with addition of water) or by injection of another oxidizing gas (for example CO ₂ ).

The oxidized layer forming on the surface of silicon or ferro-silicon is composed essentially of SiO ₂ and / or of the oxidized FeSi ₂ phase. The oxygen stoichiometry relative to the silicon of the oxide formed is typically between 1.8 to 2.5. The colors obtained are interferential colors, which vary according to the average thickness of the oxidized layer, typically between 10 nm and 1 μm.

These colors are very varied in a wide range of shades. In addition to metallic gray, it is possible to obtain the entire spectrum of colors, typically corresponding to the wavelength range: 350 nm - 800 nm. For example, we can thus obtain the following color shades: red, pink, orange, yellow, blue, green, turquoise, golden, purple, burgundy. The pigments thus obtained are stable to ambient air, to light, to alkaline and acidic media, to corrosion in saline media for temperatures less than or equal to 600 ° C. They can thus typically be used for coloring paints, lacquers or varnishes, in particular for motor vehicles, plastics, glasses, ceramics, cosmetic and decorative products. They can also find their use in paints or coatings intended to improve the behavior to corrosion, or the "antifouling" character mentioned above, by providing moreover, without other additive, the coloring.

The advantages of the invention, compared with the characteristics of the prior art, are: - The shape of the starting grains in scales, which accentuates the final shine of the product, avoids the risks of agglomeration of the grains during the treatment at temperatures up to 1350 ° C, reducing time correspondent; it finally authorizes an effective treatment of powders for the whole particle size spectrum from 1 to 250 μm. A simultaneous addition of color and metallic appearance, which can give the pigment shimmering colors, Stability in ambient air, light, alkaline and acidic environments, salt corrosion, as well as high temperature.

Examples

EXAMPLE 1 A metallurgical silicon powder, obtained after grinding in a ball mill, containing 99% silicon and having a grain size between 25 and 200 μm, was introduced into an electric rotary resistance furnace.

At 900 ° C., by oxidizing by the dry route, that is to say, in this case, at ambient atmosphere without particular addition, the following results are obtained:

Example 2

A metallurgical silicon powder, containing 99% silicon, obtained by grinding in a ball mill and having a grain size between 25 μm and 200 μm was introduced into an electric resistance resistance rotary oven.

At 1200 ° C., in the presence of air and water, injected by a metering pump at the rate of 1.0 kg of water per hour and per kg of silicon to be treated, the following results are obtained:

Example 3

A metallurgical ferro-silicon powder, containing approximately 65% silicon and 35% iron, was introduced into an electric resistance resistive oven, obtained by grinding in a bar mill and having a grain size of between 25 μm and 200 μm.

Example 4

A metallurgical ferro-silicon powder, containing approximately 65% silicon and 35% iron, obtained by grinding in a bar mill, and having a grain size of between 25 μm, was introduced into an electric resistance resistance rotary kiln. and 200 μm. At 1350 ° C., in the presence of air and water, injected by a metering pump at the rate of 1.0 kg of water per hour and per kg of silicon to be treated, the following results are obtained:

Example 5: Resistance of the colors obtained to different factors

at. Corrosion resistance in acidic and basic media

14 solutions of pH 1,2,3, ..., 14 were produced from concentrated sulfuric acid and sodium hydroxide solutions.

12 g of blue pigments, containing 99% silicon and particle size in the range 25 - 63 microns, were immersed in 250 ml of these 14 aqueous solutions. The mixture was then stirred at room temperature for 1 hour 30 minutes. After this attack time, the pigments were rinsed with water and dried at 150 ° C. in an oven. The color of the pigments has remained unchanged.

b. Resistance to corrosion in a saline environment

20 g of blue pigments, with a particle size of 25 - 63 microns, were covered with 20 g of NaCl and placed for 2 months at 150 ° C in an oven. The blue color of the pigments is not altered.

vs. Temperature resistance 20 g of blue pigments, with a particle size in the range 25 - 200 microns, were placed in an electric resistance oven for 48 h. At 600 ° C: The color of the blue pigments has remained unchanged. At 700 ° C: The color has been changed.

Claims

claims

1. Metallic pigment, having a tint by interference of light rays on its surface, or interference color, characterized in that it essentially consists of a powder of metallurgical silicon or of alloys based on metallurgical silicon containing at least 60 % by weight of metal silicon, or of a ferro-silicon powder, one or the other powder being obtained by grinding and its grains being in the form of flakes covered with an oxidized layer.

2. Pigment according to claim 1, characterized in that said scales have a length of 1 to 250 microns, a width of 1 to 250 microns and a thickness of 0.1 to 10 microns.

3. Pigment according to one of claims 1 or 2, characterized in that said metallurgical silicon contains at least 90% by weight of silicon metal, and preferably 97%.

4. Pigment according to one of claims 1 or 2, characterized in that said ferro-silicon contains between 5% and 75% by weight of iron, preferably between 25 and 35%.

5. Pigment according to one of claims 1 to 4, characterized in that the oxidized layer has an average thickness of 10 nm to 1 μm.

6. Pigment according to one of claims 1 to 5, characterized in that the color is not altered by keeping in media with pH between 1 and 14.

7. Pigment according to one of claims 1 to 5, characterized in that the color is not altered by maintaining at temperatures less than or equal to 600 ° C.

8. Pigment according to one of claims 1 to 5, characterized in that the color is not altered by corrosion in a saline environment.

. Process for treating a powder essentially consisting of metallurgical silicon or metallurgical silicon-based alloys containing at least 60% by weight of silicon, or metallurgical ferro-silicon, for obtaining said metallic pigment, characterized in that it includes the steps of: a. Preparation of a powder of metallurgical silicon or of alloys based on metallurgical silicon or metallurgical ferro-silicon, with a particle size between 1 and 250 μm, by grinding using mills typically with ball, bar or cylinder, b . Maintaining this powder at a temperature of 900 to 1350 ° C. in an atmosphere containing one or more oxidizing elements, the temperature, the duration of the treatment and the quantity of oxidizing elements being selected to obtain the desired color.

10. Method according to claim 9, characterized in that said atmosphere containing one or more oxidizing elements consists of air with addition of oxygen.

11. Method according to claim 9, characterized in that said atmosphere containing one or more oxidizing elements consists of air with the addition of water.

12. Method according to claim 9, characterized in that said atmosphere containing one or more oxidizing elements consists of air with the addition of CO ₂ .

13. Method according to one of claims 9 to 12 characterized in that the duration of the maintaining at temperature of said powder is between 1 min and 9 hours.

14. Use of the pigments according to one of claims 1 to 8 for the coloring of paints, lacquers for the automobile, plastics, glasses, ceramics, cosmetic and decorative products.

5. Use of pigments according to one of claims 1 to 8 for the manufacture of paints or anti-corrosion and / or anti-fouling materials.